Adjuncts to Local Anesthesia: Separating Fact from Fiction

• Jason K. Wong, DDS •

Abstract

Adjunctive local anesthetic techniques and their armamentaria, such as intraosseous injection, computer-controlled delivery systems, periodontal ligament injection and needleless jet injection, have been proposed to hold particular advantages over conventional means of achieving local anesthesia. This article describes the use of each technique and proprietary armamentarium and reviews the literature appraising their use.

The achievement of successful
local anesthesia is a continual challenge in dentistry. Adjunctive local
anesthetic techniques and their armamentaria are often marketed to clinicians as
a panacea, but they are not without their own disadvantages and complications.
Such techniques and equipment include intraosseous (IO) injection systems,
computer-controlled systems for delivery of local anesthetic, periodontal
ligament (PDL) injection and needleless jet-injection systems. The purpose of
this article is to review the niche applications of these techniques and to
summarize the scientific literature appraising their use.

Defining Success in Local Anesthesia

Success rates for local anesthetic techniques are critically dependent
on the particular criteria used to define success. Quoted rates may be
misleading or meaningless if they do not state the specifics of the particular
stimuli, teeth and pulpal states involved. Pulpal anesthesia as evaluated by
standard electrical pulp testing (EPT) criteria has provided a consistent basis
for elucidating the value of traditional approaches to local anesthesia as well
as the benefits of adjunctive techniques.1 Despite subjective lip
numbness, success rates for pulpal anesthesia in vital asymptomatic mandibular
first molars after conventional inferior alveolar nerve block (IANB) are poor,
averaging 69% even after deposition of up to 3.6 mL of local anesthetic2-7
(see Table 1, Success rates for conventional inferior alveolar nerve
block, ). In mandibular first
molars with irreversible pulpitis, success rates are even worse, averaging 30%8,9
(see Table 2, Success rates for conventional inferior alveolar nerve
block in patients with irreversible pulpitis, ).
Subjective lip numbness is a poor indicator of local anesthetic success as
assessed by EPT.

Reasons for Failure of Conventional Local Anesthetic
Techniques

Factors contributing to the failure of conventional local anesthetic
techniques must be considered before examining the rationale for any local
anesthetic adjunct. These factors can be broadly classified as related to the
armamentarium, the patient and the operator (see Table 3, Reasons for
failure of conventional anesthetic techniques, )
.

Armamentarium-related factors such as deflection of the needle tip have been
suggested to result in inaccurate needle placement and higher failure rates with
IANB.10 However, even with accurate placement, the unpredictable
spread of local anesthetic solution may contribute to failure.11

Patient-related factors include anatomical factors such as cross-innervation
in the mandibular incisor region12 and accessory innervation in the
mandibular posterior region (by the lingual, long buccal and mylohyoid nerves,
for example), which may allow nociceptive inputs despite complete IANB. The
thick cortex of the mandible and the zygomatic process of the maxilla impede
diffusion of anesthetic solution and may result in local anesthetic failure.
Intravascular injection invariably results in failure. Pathological states such
as the presence of pulpal inflammation are associated with higher rates of
failure of local anesthesia.13

Operator-related factors such as inexperience and poor technique may also
contribute to failure. For example, unfamiliarity with the Gow-Gates mandibular
block may lead the operator to inadvertently allow the patient to close his or
her mouth and inappropriately displace critical anatomical targets such as the
neck of the condyle out of the trajectory of the needle.

The reader is encouraged to refer to the comprehensive review articles
discussing this subject,10-13 which is beyond the scope of the
current article.

Intraosseous Injection

IO injection is the introduction of local anesthetic directly into
periradicular cancellous bone. The rationale is that efficacy will be increased
by minimizing or eliminating armamentarium, patient and operator-related factors
contributing to failure of traditional nerve block.

IO injection has been purported to result in greater success of anesthesia,
more rapid onset of anesthesia, and less residual soft-tissue anesthesia; it is
apparently less painful and reportedly allows use of lower doses than are needed
for conventional nerve block techniques. In virtually all studies investigating
these claims (and cited in the following paragraphs), the Stabident system has
been arbitrarily selected for analysis.

When used to supplement failed primary IANB, IO injection has reliably
increased success2,4-6,8,9,17 (see Table 5, Success rates for
conventional inferior alveolar nerve block with supplemental intraosseous
injections, and Table 6, Success rates for conventional inferior alveolar
nerve block with supplemental intraosseous injection in irreversible pulpitis,http://www.cda-adc.ca/jcda/vol-67/issue-7/391.html
In the cited studies,
success was defined as no response to maximal EPT output (80 readings) on 2
consecutive tests 60 minutes after application of the anesthetic. Supplemental
IO injection improved the average success rate to 97% in vital asymptomatic
mandibular first molars2,4,5,6,17 (Table 5) and to 83% in
first molars with pulpitis8,9 (Table 6). However, anesthesia
declined to as low as 76% after one hour.12

IO injection is less successful as a primary technique in mandibular first
molars, for which success rates average 75%18,19 and decline steadily
with time to less than 50% after one hour.18 This method appears to
have no advantages over IANB as a primary means to achieve anesthesia.

Claims that anesthesia is immediate are fairly consistent with clinical
findings. Onset of anesthesia has been within one minute after injection and
therefore can be deemed rapid, if not immediate.2,4,6

Maximal discomfort was rated as mild to moderate pain and occurred on
insertion of the needle for infiltration before perforation, rather than during
the perforation itself (which was rated as causing no discomfort or as mildly
painful).18 This effect is attributed to the absence of sensory
innervation in cortical bone, in contrast to the richly innervated periosteum.18

The duration of anesthesia is less with plain solutions than with
vasoconstrictor.2,19 According to the single study available, there
appears to be less soft-tissue anesthesia (42%) with primary IO injections
compared to IANB.18

Claims have been made that reducing the volume of local anesthetic
injected does not affect the success rate of the IO approach. Only the
supplemental IO injection has been studied in this respect. It appears that
reducing the volume from 1.8 mL to 0.9 mL does not appreciably reduce success.4,17
There have been no studies of potential differences in anesthetic success with
reduced anesthetic doses in primary IO injection.

IO injection is advantageous in specific clinical situations, such as
treatment of patients with coagulopathy, in whom the risk and consequences of
hematoma through nerve block anesthesia are significant; bilateral restorations;
and treatment in which residual soft-tissue anesthesia is especially
undesirable.

Increases in heart rate have been subjectively and objectively measured in
approximately 74% of patients after IO injection of 18 µg of epinephrine.2,6,9,18,20
Mean increases were approximately 24 beats/minute, and heart rate returned to
baseline within 4 minutes in over 85% of subjects.6 Increases in
heart rate are of little clinical significance in healthy patients6
unless patients interpret them as emotionally or psychologically disturbing. In
this case, plain solutions (such as 3% mepivacaine without vasoconstrictor) are
acceptable alternatives, since no subjective increases in heart rate have been
reported with their use.5,6 For similar reasons, it may be prudent to
use solutions without vasoconstrictor for any patient with cardiovascular
disease for whom the proposed procedure is appropriately brief.

Reported postoperative complications include perceived hyperocclusion (6%)2,6,18
and infection at the site of perforation (3%).2,18

If the patient has narrow attached gingiva at the proposed site of IO
injection or has severe periodontal disease, IO injection is contraindicated.18,20

Computer-Controlled Systems for the Delivery of Local
Anesthetic

The Wand (Milestone Scientific, Livingston, NJ) is a
computer-controlled pump modelled after those used in intravenous administration
of general anesthetics (Table 4;Fig. 4). It can deliver a
constant volume of anesthetic at constant pressure, which purportedly enables
less painful delivery of the anesthetic. This claim is based upon the premise
that pain due to local anesthetic injection is attributable to factors such as
fluid pressure on injection and flow rate. Other purported advantages include
greater tactile sensitivity and less intrusive appearance. Relative
disadvantages are higher cost and speed of injection — at the slowest pump
rate, a total of 4 minutes is required to completely express a cartridge.

In a blinded, controlled trial, Asarch and others21 showed no
difference in pain ratings, pain behaviour or overall satisfaction with dental
treatment in pediatric patients receiving infiltration, IANB and palatal
injections with the Wand and a conventional syringe technique. There are few if
any other unbiased blinded, controlled trials upon which to base any conclusions
regarding the benefits of computer-controlled delivery systems.

Two other computer-controlled delivery systems have been recently released:
the Comfort Control Syringe (Midwest-Dentsply, Des Plaines, IL) and the
Quicksleeper (Dental Hitech, ZI Champ Blanc, France).

Periodontal Ligament Injection

PDL injection is also known as intraligamentary injection,
transligamentary anesthesia and intraperiodontal anesthesia. Originally
described in 1924, its application has since been the impetus for the design of
specialized syringes, including the N-Tralig (Miltex Instrument Company, Inc.
Bethpage) (Table 4; Fig. 5), the Ligamaject (Healthco Inc.,
Boston, MA), and the Peripress (Universal Dental Implements, Edison, NJ).

The term PDL injection is something of a misnomer. With this technique,
anesthetic fluid spreads primarily along the outer surface of the alveolar plate
and under the periosteum, moving into crestal marrow spaces along vascular
channels and not through the PDL as previously assumed.22 Therefore,
what is termed PDL injection should be considered a form of IO injection.22

The technique involves use of a 25- or 27-gauge short needle or a 30-gauge
ultrashort needle.15 Empirical evidence suggests that longer,
smaller-gauge needles are more apt to buckle on insertion; however, PDL
injection has been performed successfully with all needle lengths and gauges in
both standard syringes and specialized pressure syringes (Fig. 5).15

The most objective measure of success — the onset, duration and rating of
pain associated with primary PDL injection — is response to EPT (where success
is defined as no response to maximal EPT output).23,24 The following
discussion applies to mesial and distal injections (0.2 mL of 2% lidocaine and
1:100,000 epinephrine for each injection) with a Ligamaject syringe.

Onset of anesthesia is rapid, if not immediate (within 2 minutes of
completion of the injection).23 For a primary PDL injection, the
success rate at 2 minutes was 79% in mandibular and 75% in maxillary first
molars.23 However, the success rate at 2 minutes was only 18% in
mandibular and 39% in maxillary lateral incisors.23 In addition,
success rates declined with use of plain solutions.24

When PDL injection was used as a supplement to conventional IANB, the success
rate was 78% for first molars. This improvement was maintained for approximately
20 minutes, after which success was similar to that observed with IANB alone
(63%).7

Duration of anesthesia is brief for the primary PDL injection (combination of
0.2 mL for the mesial injection and 0.2 mL for the distal injection), with only
20% of mandibular and 25% of maxillary first molars anesthetized 10 minutes
after injection, and only 10% of mandibular and 30% of maxillary later incisors
anesthetized at this time point.23 It is not clear whether use of
0.5% bupivacaine significantly prolongs the duration of anesthesia with primary
PDL injection.25

Without topical anesthetic, insertion of the needle itself is rated as mildly
to moderately painful and generally contributes to most of the perceived
discomfort.23 Needle insertion is more painful in PDL injection for
anesthesia of the maxillary lateral incisor than for other teeth.23

The ability of PDL injection to produce anesthesia of a single tooth is
unpredictable, and therefore its use as an aid in endodontic diagnosis is
questionable.26

The distribution of injected solutions is primarily intraosseous and
perivascular, and rapid systemic absorption is likely.27
Cardiovascular effects such as changes in mean arterial pressure and heart rate
were similar for PDL, IO and intravenous injections of 3 µg of epinephrine in
dogs (0.3 mL lidocaine 1:100,000).27

Postoperative sequelae are common but self-limiting.23,24 Pain of
mild or moderate severity was reported by 83% of patients after 24 hours.23
Hyperocclusion was reported by 36% of patients after 24 hours and by 7% after 3
days.23 Swollen interdental papillae were reported by 13% of
patients.23

Damage to the crestal bone and cementum from needle trauma is possible, but
is minor and reversible.28 Epithelial and connective tissue
attachment to enamel are not disturbed by needle puncture.29
Injection of the solution is not damaging. Pulpal changes after PDL injections
are mild and reversible.30

Needleless Jet-Injection Syringe Systems

First described in 1866, jet-injection devices were originally
developed for mass immunization. Modern designs have been approved for
intramuscular and subcutaneous delivery of medications such as hepatitis B
vaccine and insulin.31

Needleless jet injectors such as the Syrijet Mark II system (Mizzy Inc.,
Cherry Hill, NJ) are marketed for use in the dental setting (Table
4; Figs.
6a,6b,6c). Acceptance of this needleless instrument is high among
adult (90%)32 and pediatric (75%) populations.33
Situations in which this system might be appropriate include placement of rubber
dam clamps, placement of retraction cords, creation of drainage incisions for
abscesses, and placement of orthodontic bands or space maintainers.

Controlled studies evaluating efficacy are lacking, and reports are primarily
anecdotal. Soft-tissue anesthesia, determined by probing unattached gingiva, was
reported as “good.”34 The success rate for pulpal anesthesia of
permanent maxillary lateral incisors was poor (13%), as assessed by pulp tests34;
however, Saravia and Bush33 reported that anesthesia during 11
extractions of deciduous teeth and 2 pulpotomies was completely successful in a
group of children averaging 10 years of age.

Adverse effects are rare. There has been one report of clinically significant
hematoma formation after jet injection with the Syrijet.35

The advantages of needleless systems for delivery of local anesthetic include
rapid onset of anesthesia, predictable topical anesthesia of soft tissues,
controlled delivery of anesthetic dose, obviation of needle-stick injury,
obviation of intravascular injection and high patient acceptance, especially in
instances of needle-phobia. The disadvantages are cost, the potential to
frighten patients with the sudden noise and pressure sensation that occur on
delivery of the anesthetic, the intrusive appearance of the device, the
possibility of small residual hematomas, leakage of anesthetic and questionable
efficacy for pulpal anesthesia.

Conclusion

IO injection provides profound anesthesia for 60 minutes when used as
a supplement to failed IANB. This is an appropriate alternative primary
technique for procedures of short duration (less than 20 minutes) and in
situations in which residual soft-tissue anesthesia is undesirable or nerve
block carries a significant risk of hematoma. An increase in heart rate
comparable to that experienced with mild exercise should be anticipated and is
of little consequence in healthy patients.

Computer-controlled delivery systems have not been demonstrated conclusively
to afford less painful delivery of local anesthesia relative to conventional
syringes.

PDL injection may be performed equally well with conventional syringes and
pressure syringes. When used as a primary technique, both methods are just as
effective as conventional IANB in achieving pulpal anesthesia, but the duration
of action is much shorter. PDL injections are most effective in supplementing
failed IANB. Postoperative sequelae such as soreness at injection sites are
common but transient.

Jet-injection systems appear to represent an effective alternative means to
achieve topical anesthesia of oral mucous membranes. Their use in effecting
pulpal anesthesia is questionable. Relative drawbacks include a potentially
startling discharge of compressed gas. The primary advantages include obviation
of needle-stick injuries and much better patient acceptance than for needle
delivery.

In conclusion, knowledge of adjunctive anesthetic techniques may broaden the
dentist’s ability to provide appropriate local anesthesia. It is important to
critically evaluate any new method to determine its merit. Techniques with
proven value may provide a beneficial supplement to traditional means of
achieving local anesthesia.

Acknowledgments: The material in this manuscript was
presented in part at the University of Toronto’s faculty of dentistry clinical
conference series on anesthesia in January 2000. The author thanks Drs. Shawn
Jacobs and Daniel Haas for assistance in preparation of this manuscript.

Dr. Wong is a senior resident in the graduate anesthesia program,
faculty of dentistry, University of Toronto.

35. Tabita PV. Side effect of the jet injector for the production of local
anesthesia. Anesth Prog. 1979; 26(4):102-4.

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